This invention relates generally to a rotary electromagnetic machine. More particularly, this invention relates to cooling of a rotor for an electromagnetic machine.
An electromagnetic machine typically includes a rotor rotated relative to a stator. Such electromagnetic machines convert mechanical energy to electricity or convert electricity to mechanical energy.
Generators typically use a rotor mounted within a stator. The rotor is driven to rotate relative to the stator to create electrical energy. A power generating device that provides increased electrical power output typically utilizes a rotor winding rather than a permanent magnet-type electric generator. The rotor winding becomes an electromagnet when the winding is connected to a current source. An electromagnet produces a rotating magnetic field of sufficient intensity to generate the desired amount of electrical power. The rotor winding generally comprises a plurality of coils wound around a magnetic core.
Generators produce heat through resistance loss in the rotor and stator winding, eddy currents within the stator and rotor cores, and friction between bearings and the fluid between the rotating and stationary components. The rotor and stator are typically cooled by a coolant fluid such as oil or a cool gas. Heat generated and produced by a generator reduces efficiency and limits generator output.
Increasing the electrical power output from a generator is typically accomplished by increasing the diameter or length of the rotor, or by increasing rotor speed. However, as the diameter, length and speed of the rotor is increased, the heat generation caused by electrical resistance and other mechanical interactions increases.
It is known to cool a rotor by flowing coolant through a hollow shaft into a magnetic core. Fluid within the magnetic core is then dispersed and driven radially outward by the centrifugal force generated by rotation of the rotor. Disadvantageously, as the rotor core increases in size to provide increased power generation, the cooling efficiency of conventional coolant passages is not sufficient to provide a desired cooling level.
Increasing rotor speed creates the additional challenge of supporting and containing electrical windings that are disposed toward ends of the rotor core. Forces caused by rotor rotation push the end windings radially outward. Typically, a continuous band of high-strength material is provided over the end turns at each end of the electromagnetic winding to contain the movement of the winding end turns. An additional method used on higher speed rotors is the inclusion of a continuous sleeve over the core and both the winding end turns. The sleeve is also of a high-strength material, such as a continuous wound fiber composite or super high-strength material, and it is provided to support and contain the core and the end windings. The addition of the sleeve over the core can result in an undesirable increase in the magnetic air gap between the rotor and the stator that can have adverse affects on power generation.
Accordingly, it is desirable to develop and design a generator having coolant passages that cool a rotor core more efficiently to accommodate increased power generation and rotors of increased size.